Coating processes for metal surfaces are known, in particular for strip, wire or metal bars, using a coating metal such as for example zinc, aluminum, tin, lead or a combination thereof, or other metal materials.
In the following description reference will be made to the specific case of coating a metal strip even if this does not exclude that the present invention can also be applied to other types of metal products such as for example bars, wire or other.
The coating processes provide to immerse the strip in a molten bath of coating metal, obliging it to wind under a certain tension at least partly around a roll that is supported at its two ends by respective support bearings.
Both the roll and the bearings are completely immersed in the metal bath by a support arm. Upstream and/or downstream of the winding roll, also immersed in the bath, there may also be other pairs of traction and/or guide rolls.
Various solutions are known of bearings used in the state of the art. For example a solution is known in which each of the support bearings comprises a first external ring that is located in a housing seating associated with the support arm, a second ring disposed inside the first, which is mounted on an end pin of the roll, and a plurality of rolling elements, substantially cylindrical in shape, disposed parallel to each other in the interspace defined between the first and second ring.
A cage-type containing structure, also interposed between the first and second ring, supports the rolling elements during use, and keeps them with their respective axes parallel to the axis of rotation of the roll.
In the specific case of coating processes with metal, the different parts of the bearings are subjected to a high level of wear, which entails the need for frequent interventions to replace them, and consequently the plant must be stopped.
The geometry and wear of the bearing may cause the rolling elements to seize, and therefore also the bearing and the roll, which in turn, being prevented from rotating, damages the surface of the strip to be coated and generates in the strip unwanted vibrations that entail a non-uniform thickness of the metal coating that is applied.
The thinner the metal strip to be coated, the more serious this disadvantage is. In fact, a thin strip is kept under tension with a lower value than a strip with a greater thickness. In this case, in fact, a sufficient reciprocal friction force between roll and strip is not guaranteed, which is necessary to overcome the resistance torque exerted by the bearing, with consequent slipping that damages the surface.
As the thickness of the strip to be coated increases, the greater the tension to which the strip is subjected, the greater are the stresses to which the bearing is subjected, and therefore the more rapid the process of wear will be.
These problems of wear are even more accentuated by the presence of impurities in the metal bath, also known as dross, consisting for example of intermetallic compounds such as oxides of Fe, Zn and Al. These compounds act on the parts of the bearing like abrasive powders which, entering between the interstices of the bearing, cause it to seize and also cause a rapid wear thereof.
Another disadvantage is that, due to the high reactivity of the molten coating metal into which they are immersed, and the high working temperatures, the various parts of the bearing are subjected to a rapid process of corrosion, which generates other impurities in the bath.
Another disadvantage is that the movement members of the strip, due to the friction that increases in the bearing, are subjected to an increase in the drawing power required to feed the strip forward.
From the Japanese patent JP-A-8028575, a bearing is known for the planetary gear of a reducer mechanism in which a support made of resin contains a plurality of rolls that are engaged by protuberances made on the inner walls of the support and small pits made at the two ends of each roll.
From the German patent DE-A-102008005376 a bearing is known with a structure consisting of two circular crowns held at a distance by connection elements and between which the rolling elements are located. Each end of each rolling element has a cylindrical shape and is housed in a corresponding radial seating made in one of the two circular crowns. Shaped elements contribute to define each radial seating and function as attachment members. The inner crown is provided with two raised parts, between which the rolling elements are held in position. This bearing has the disadvantage that the radial seatings for the ends of the rolling elements are indeed made through, but are completely occupied by the ends themselves, which are cylindrical. Indeed, the play between the cylindrical ends of the rolling elements and the corresponding cylindrical radial seatings is such as to allow the rotational motion of the first with respect to the second, but not such as to allow the passage and reflux of the coating liquid.
From the Japanese patent JP-A-2006-177485 a bearing is known that comprises a structure in which rolling elements are disposed, equidistant and radial, the ends of which are housed in the corresponding forms of the structure, allowing a certain play and hence the presence of lubricant.
From the European patent EP-A-1 826 424 a support bearing for a roll is known, suitable to be immersed in liquid metal, comprising a rotating internal bushing mounted coaxial on an end pin of the roll and in rotation inside an external bushing attached to a support arm. Clamping elements are also provided to prevent the bearing from exiting axially from its seating and from rotating in the seating.
One purpose of the present invention is to obtain a support bearing for a roll that can be used in an environment under severe functioning conditions, in particular from the viewpoint of chemical aggression and the high working temperature, and therefore has a long working life compared with bearings known in the state of the art.
Another purpose of the present invention is to obtain a bearing to support a roll which, during functioning, has a smaller resistant torque compared with known solutions.
Another purpose of the present invention is to obtain a roll associated with support members that allows over time to reduce the energy consumption needed to move the strip.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.